Ultra-short pulse sources have had a major impact on laser-based technology during the last decade. Applications include imaging, micro-machining and ophthalmology. Because of their unique stability, compactness and ease of construction, fiber laser based ultra-short pulse sources have started to dominate the ultra-short pulse source market segment. Exemplary ultra-short pulse sources are described in U.S. Pat. Nos. 8,031,396; 7,688,499; 7,167,300; 6,885,683 and 5,696,782. In order to be able to address many industrial applications, pulse sources producing pulse widths ranging from sub picosecond to 10 ns are highly desirable, where in order to minimize cost, preferably, these systems are based on the same technology platform.
Modelocked fiber lasers are an attractive source for producing pulses in the fs to ns range, where further amplification in fiber amplifiers can be implemented to reach pulse energies up to the mJ level. Thus, an all-fiber system construction can be achieved.
One limitation of all-fiber systems is the relatively low pulse energies of mode-locked fiber oscillators. Several fiber amplification stages may be required to reach high pulse energies. Another limitation arises from the requirement of linear amplification stages as, for example, encountered when implementing chirped pulse amplification systems, which limit the achievable peak power from fiber amplifiers. As the pulse energy and/or peak power is increased, chirped pulse amplification further requires complex schemes for pulse stretching and compression with precisely matched values of dispersion. On the other hand, when nonlinear fiber amplifiers are employed, the pulse quality can be detrimentally affected when implementing pulse compression stages after the nonlinear fiber amplifiers.
Gain-switched diode-based laser systems or micro-chip lasers have been implemented as front ends to fiber amplifiers to circumvent the limitation of all fiber systems, but so far with limited success. For example, it is generally very difficult to generate bandwidth-limited pulses from gain-switched diode lasers in the pulse width range from 10 ps-1 ns, and also the generation of pulse width tunable systems with pulse widths around 100 ps is relatively complex. As other examples, continuous wave emitting diode lasers have been suggested as a solution to pulse width tunable short pulse laser systems (U.S. Pat. No. 7,330,301 to D. J. Harter et al.). Arrangements of pulse shortening stages implemented in conjunction with micro-chip lasers can require relatively complex schemes to minimize pulse jitter. For example, see A. Steinmetz et al., Sub-5-ps, multimegawatt peak-power pulses from a fiber-amplified and optically compressed passively Q-switched microchip laser, Optics Letters, Vol. 37, Issue 13, pp. 2550 (2012).